<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #talkbubble {
            width: 120px;
            height: 80px;
            position: relative;
            -moz-border-radius: 10px;
            -webkit-border-radius: 10px;
            border-radius: 10px;
            border: 1px #808080 solid;
            background-color: #fff;
        }
        #talkbubble:before {
            content: " ";
            position: absolute;
            top: 100%;
            left: 50px;
            width: 0;
            height: 0;
            border-left: 15px solid transparent;
            border-top: 15px solid #808080;
            border-right: 15px solid transparent;
        }
        .inlayer:after {
            content: " ";
            position: absolute;
            top: 100%;
            left: 51px;
            width: 0;
            height: 0;
            border-left: 14px solid transparent;
            border-top: 14px solid #fff;
            border-right: 14px solid transparent;
        }
        #talkbubble:hover {
            background-color: #ff0000;
        }
        .inlayer:hover:after {
            width: 0;
            height: 0;
            border-left: 14px solid transparent;
            border-top: 14px solid #ff0000;
            border-right: 14px solid transparent;
        }
    </style>
</head>
<body>

<!-- html -->
<div id="talkbubble" class="inlayer">
    空心三角形
</div>
</body>
</html>